The invention relates to replacement cartridges for full face and half mask respirators containing service life indicators.
It is known in the prior art to provide end of service life indicators for replaceable chemical filter cartridges that are used with respirators. For example, U.S. Pat. No. 4,326,514 discloses a cartridge into which is fitted a web or strip that is treated to undergo a color-changing reaction when it is contacted by the type of toxic chemical contaminant(s) for which the respirator is to be used. Since it is taught to extend the strip around all or most of the interior wall surface, this approach can add a significant cost to the manufactured cartridge. Furthermore, the potential for the formation of channels, cracks and non-conformities in the filter bed adjacent the strip can lead to wide variations in the rate of advance of the color changing line and the inability to accurately evaluate the true condition and capacity of the filter to retain or neutralize the contaminant. These problems may explain why this approach does not appear to have been adopted by cartridge manufacturers.
It is also known from the prior art to apply a web or strip such as that described above to the exterior surface of the cartridge so that the color-changing indicator reaction is initiated as soon as the wearer enters an environment containing a toxic chemical with which the indicator is reactive. This approach suffers the drawback of providing only an approximation of the condition of the chemical sorbent material inside the cartridge, and in practice, it has been found that this exterior-mounted indicator has completed its color-change long before the cartridge has reached the end of its useful service life, thereby resulting in the premature changing and disposal of the cartridge. It is also the practice to extend the strip or web of the color-changing indicator around the entire periphery of the cartridge, since the indicator strip must be visible to the wearer when the cartridge is in place on the face mask and the orientation of the cartridge is random when it is threaded onto the mask mounting means. Thus, a much greater length of the indicator strip material than is actually viewable must be applied to each cartridge.
Another means for providing a color-changing indicator for a respirator cartridge is disclosed in U.S. Pat. No. 4,154,586 and U.S. Pat. No. 4,530,706, where the interior of the cartridge is provided with a plurality of compartments in a vertical array, each compartment containing a color-changing indicator material that is visible through the transparent sidewall of the cartridge that also defines one wall of the compartments. The indicator material is separated from the filter sorbent bed by a sidewall. The upstream end of the chamber is covered by a perforated top wall and airborne contaminant travels through the chamber in a path that is parallel to, but separated from the air entering the filter medium. The rate of change of color in the separate chamber is intended to correspond to the condition of the filter medium in the adjacent bed. It is not clear from the disclosure how this relationship is to be attained, particularly if the cartridges are to be mass produced. The construction of cartridges in accordance with these disclosures by molding or otherwise would be complex and expensive. Furthermore, it is not at all clear how a uniform, consistent and reliable product could be mass produced, since the packing or filling of the chambers to a uniform density and compaction in production quantities is not apparent.
It is therefore an object of this invention to provide an improved replacement cartridge and a method for its manufacture that includes a reliable color-changing ESLI with a visual display field that provides for a predetermined margin of safety.
Another object of the invention is to provide an improved replacement cartridge that includes an ESLI, which cartridge can be manufactured economically, that is reliable and consistent in performance and that utilizes components of otherwise conventional construction.
A further important object of the invention is to provide an improved replacement cartridge that incorporates a clearly delineated color-changing indicator display field that permits the wearer of the respirator mask to adjust the position of the installed cartridge so that the display field can be viewed during use.
The above objects and other advantages are achieved with the present invention in which a replacement respirator cartridge is provided with an improved end of service life indicator, or ESLI. In one preferred embodiment, the cartridge is provided with a display window defined by an opaque border positioned on the sidewall and a chemical sensor having a color-changing display field is secured in position against the interior surface of the sidewall with the display field at least partly aligned with the display window. The sensor can be a deformable, relatively thin, laminated structure having one exterior sidewall that is transparent and through which a color-changing chemical material can be viewed; the opposite wall is formed from a vapor-permeable material through which contaminant molecules, gas and/or vapor can pass to initiate the color-changing reaction.
The color-changing sensor is securely positioned against the interior surface of the sidewall, as by adhesive applied to a portion of the sensor surrounding the color-changing display field. The sidewall of the cartridge is transparent, in at least the area of the display window where the sensor is secured in position.
The permeable sidewall of the sensor is contacted by the activated carbon or such other filter medium as fills the body of the cartridge. In a particularly preferred embodiment, the relative positions of the display window and the display field with respect to the downstream portion of the filter bed are prescribed in order to provide a predetermined minimum margin of safety for the use of the cartridge. For example, assume that the cartridge is rated as having a total useful service life of sixty minutes in a given concentration of contaminant gas by a user expressing average breathing rates and lung capacity. If the sensor extends vertically through 90% of the upper or upstream end of the filter bed, and a 25% safety margin is to be provided for the particular contaminant, the display window is provided with an opaque border that masks the lowest 25% of the filter bed sidewall and covers 15% of the downstream end of the sensor. If a greater or lesser safety margin is desired, the width of the opaque border, or its position relative to the downstream end of the filter bed and or sensor can be adjusted accordingly.
In a preferred embodiment of the invention the sensor is closely-fitted and secured to the interior surface of the shell""s sidewall. In one preferred embodiment, the sensor can be secured by adhesive which is provided around the periphery of the display field and covered with a releasable film or strip prior to placement on the sidewall. In an alternative embodiment, (not shown), the sensor is mechanically secured in position at the interior surface of the sidewall, as by one or more spring clips, a retaining bracket or parallel channels affixed to the interior sidewall. In yet another embodiment (not shown), a reactive color-changing composition is formulated into a coating composition that is applied directly to the interior of the sidewall. The composition can be formulated in a polymeric latex or other suitable material that will adhere securely to the wall and permit the color-change to be clearly visible.
Regardless of the means employed for securing the sensors, it is important that the sensor remain in the desired position without movement during use and that it be maintained in intimate contact with the adjacent filter medium without channels or other irregularities, discontinuities or the like to interfere with the uniform migration of contaminants through the adjacent bed and into the permeable wall of the sensor.
In another aspect of the invention, an apparatus and method for mounting the improved ESLI cartridge on the respirator mask provides means for continuously rotating the sealed cartridge to properly align the ESLI sensor for viewing. A continuously rotatable mounting for the cartridge is required to allow the wearer of the respirator to move the color-changing sensor into the wearer""s field of view. If the cartridge is attached to a full face mask, the sensor will have to be viewed through the transparent portion of the respirator facepiece. Since the cartridge must be mounted on a male threaded member that is an integral part of the respirator cheek area, for safety reasons it must not be possible for the wearer to unscrew the cartridge as might be required to bring the sensor into the field of view, since unscrewing the cartridge would break the air seal and allow possibly contaminated external air to by-pass the filter cartridge.
In order to avoid this possibility and to permit rotation while at the same time maintaining a secure air-tight seal, a multi-part mounting assembly that includes a rotating seal is provided to thereby permit the cartridge to be rotated continuously in the direction used to install the cartridge, traditionally, the clockwise direction. In one preferred embodiment, a ratchet assembly is employed and the detents or ratchet teeth are molded into the interior surface of the cartridge shell. A threaded flanged insert is placed into the projecting collar portion of the cartridge shell, and the flange is divided into a plurality of segments, each of which segments includes a pawl that engages corresponding teeth formed in the interior surface of the cartridge housing surrounding the threaded collar opening. As in any ratchet, the pawls allow the flange to rotate freely in one direction, but engage the teeth when rotated in the opposite direction, thus causing both members of the assembly to rotate together when it is desired to unscrew and remove the cartridge from the respirator mounting means.
Since the flanged insert must be free to rotate against the cartridge housing, it is necessary to provide an air seal against leakage of contaminated air into the respirator at the point of attachment of the cartridge. In a preferred embodiment, a mechanical seal is provided between the members of the assembly. In an especially preferred embodiment, this sealing is accomplished by providing the internal rim of the neck of the cartridge housing with a rounded projecting bead seal and the adjacent exterior surface of the flanged insert with a corresponding concave seat. The flanged insert is produced from a plastic composition having the requisite deformation and resilience properties that permit it to be press-fitted into the neck portion of the cartridge so that the seal engages the seat.
To complete installation of the respirator cartridge on the mask, the cartridge is screwed onto the male threaded member projecting from the cheek of the respirator until the clicking of the ratchet members is heard. This audible signal assures the wearer that the cartridge has been properly installed, since the threaded members will bring the ratchet assembly into contact only when the male and female threads are properly engaged. This also assures the wearer that the proper seal has been achieved between the respirator and the cartridge. After donning the respirator, the cartridge can then be further turned in the clockwise/tightening direction until the sensor is in the wearer""s field of view, the wearer being assured that the cartridge is being turned in the correct direction by the audible clicking sounds. When the cartridge is turned in the counter-clockwise direction, the pawls engage the notches and the cartridge can be removed for replacement.
The present invention provides the user of the respirator to which the cartridges are attached a clear indication of the extent to which the activated carbon contained in the cartridge is being contaminated, and conversely, how much active material is remaining. This is very important to the user, because the life of the cartridge and its contents depends on many variables, including the concentration of the contaminant in the physical area of the user; the rate at which the user is breathing; and the capacity or air volume of each breath. Obviously, a worker exerting himself under strenuous conditions will require considerably more air to sustain himself than a worker in a control booth who may only be monitoring instruments.
In a preferred embodiment, a lower portion of the color-changing sensor adjacent the downstream end of the carbon bed is not visible through the viewing window in the label, thereby providing a margin of safety or time during which the cartridge can continue to function to remove contaminants. The vertical dimension of the display field of the sensor in contact with the carbon bed can be varied in accordance with use requirements and the vertical dimension and position of the viewing window relative to the sensor and/or the bed can be varied to provide a predetermined margin of safety.
It is to be noted that the invention is described with reference to a xe2x80x9ccartridgexe2x80x9d filter, which is to be understood as being distinguished from a xe2x80x9ccanisterxe2x80x9d filter by its somewhat small size and direct attachment to a so-called full-face or half-mask. As will be apparent to one of ordinary skill in the art, the invention can be used in any size filter, where the sensor can be secured in intimate relation with a longitudinal section of the filter bed and viewed through an adjacent transparent display window.
Thus, in its broadest aspect, the improved ESLI cartridge of the invention comprises a cartridge shell that is transparent in at least the area of a sidewall at which the color-changing sensor is placed; the chemical sensor is secured to the interior surface of the sidewall of the cartridge, one side of the sensor having a visually perceptible indicator that forms a display field, preferably a color-changing indicator, the opposite side of the sensor being in touching contact with the activated carbon bed or other filter medium that is packed in the cartridge; a display window defined by an opaque border, where the display window corresponds to at least a portion of the vertical section of the display field of the color-changing sensor; and means for maintaining a seal and means to permit the cartridge to be continuously rotated so that the sensor can be viewed by the wearer of a mask to which the cartridge is attached to bring the sensor into the wearer""s field of vision.